Analog memory systems



Oct. 8, 1963 J. A. EBY 3,106,704

ANALOG MEMORY SYSTEMS Filed Aug.v 29, 195o f JUFPL V Z INVEN TOR.

ByC/

3,106dfi Patented @et 3,` 1963 :Mil/m4 ANALG MEMRY SYSTEM@ .lames A. Eby, Canoga llarlr, Calif., assigner to Electro- Mechanical Research, liuc., sarasota, Fia., a corporation of Connecticut Filed Aug. 29, 1960, Ser. No. 52,667 3 Claims. (Cl. 34h-4F74) This invention relates to analog memory systems and more particularly to memory systems employing magnetic circuit elements having a generally rectangular hysteresis characteristic.

For purposes of sampling the 'analog outputs of transducers, particularly for remote telemetering of their outputs, a time multiplexing is often desirable. lf continuous indications are to be obtained of these outputs, especially with Aa moderate sampling rate, storage of a sampled output between successive intervals is necessary. In the past such storage has ten-ded to require relatively complex and expensive apparatus or has been characterized by decay of stored values.

Accordingly, it is `an object of the present invention to provide new and improved analog memory systems wherein storage of analog values may be obtained with no decay or loss of stored values.

Another object of lthe invention is to provide such systems which are highly reliable, require relatively simple and inexpensive apparatus and are adaptable to a wide variety of applications.

t ese and other objects are achieved, in accordance with the invention, by the use of a variable transformer, referred .to herein Ias a transiluxor, comprising a core of substantially rectangular hysteresis material having at least two apertures defining three legs. A first leg carries a control winding and a third leg carries primary and secondary windings having an inductive coupling dependent upon ilux density and direction in Ithe intermediate 0r second leg. Periodic current from a reference supply is applied to the primary winding, and an output signal is obtained from the secondary winding dependent upon the coupling established by the passage of current through the control winding.

By controlling the current momentarily applied to the con-trol winding by an excitation circuit as a function of a data input signal (and preferably also in degenerative relation to the output signal applied to the excitation circuit by way of a feed-back loop), the output signal is reset to a value corresponding to said data signal.

When the data signal is time multiplexed, separate transluxors may be driven continuously by a common reference supply for .the primary windings and sequentially by a common excitation circuit for the control windings.

The invention, together with others of its objectives and advantages, will be more fully understood from the following detailed description, taken in conjunction with the drawing, in which:

FIGURE l is a block diagram the invention; and

FIGURE 2 is a block diagram representing a rnodication of the apparatus of FlGURE l, suitable for multichannel applications.

ln FIGURE 1 an input signal voltage V1 is applied at terminal lil via switch lll to one input terminal of a balance or differential ampliiier l2, with respect to` a ground or reference point. Across the output terminals of the amplier l2 is connected a switch l and a control ywinding M in series. The amplifier thus applies a control signal voltage E to the control winding le of what is termed a transiluxor, when the switch 13 is closed.

The transfluxor is described more particularly in an article by Rajchman and Lo entitled The Transiluxor appearing in the Proceedings of the iRE, March 1956.

of apparatus embodying For purposes of the present invention, however, the transliuxor may be understood as a variable transformer comprising a magnetic core i6 composed of material such as lferrite having a substantially rectangular hysteresis characteristic. The core lo may be of relatively thin cylindrical form having an excentered main aperture l? and a secondary smaller aperture lll? oiset from the main aperture in a direction opposite from the direction of excentering of the main aperture so as to define a rst leg 2l,

a second leg 22, and a third leg 213. Preferably the cross sectional area of the rst leg on the excentering diameter is equal to the sum of the cross sections of legs 22` and 23, the latter being substantially equal. Hence an inner annular ux path encircles main aperture l? via legs 2l and 22 when current is passed through control winding le, and another Flux path is provided by legs 22 and 23 encircling aperture l@ for purposes of inductively coupling a primary winding 7,5 and a secondary winding 26 carried by leg Z3.

A periodic reference signal of constant value, such as an alternating current at 50 kc., is applied to primary winding 25` by AC. supply Such current is of an amplitude less than that which would produce saturation in the ilux path about aperture i3. The terminals of the secondary winding are connected to a rectilier 29 which may, for example, comprise an emitter-follower rectifying ampliiier operating in Class C and a resistance-capacitance low-pass iilter circuit of suitable time constant for respectively rcctifying and fil-tering the 50 kc. signal induced in the output winding. To obtain indications of the rectified output winding signal corresponding in value to the input signal V1, there is connected across the output terminal of rectifier 29 yan output meter Sti which may be in series with a suitable resistor 3l across which the output voltage V0 to be measured is developed.

Because the r-ansfer characteristic between the control winding llland the output win-ding 26 varies non-linearly and as a function of such variables as the ambient temperature, the exact characteristics of the core material, and the physical dimensions of the core itself, it is ditiicult to provide 4a calibration of the output which is independent of the particular core and ambient conditions. Hence, there is provided, in accordance with the invention, a feedback loop trom the ungrounded side of the output resistor 3l through a switch 33 to the other input terminal of diierential amplifier' l2. Accordingly, the differential amplitier is responsive to AV: T/-l/.c or the error signal between the output and input applied whenever switches 1l and 33 are closed in common.

It may be noted that Class C operation of :the rectifying amplifier resul-ts in a DC. current output which is exactly comparable to the input signal at the instant of sampling. Also, while a common conne-ction has been shown for concurrent closure of switches ll, i3 and 33, switch 13 need not be closed for the full interval for which both switches 1l .and 33 are closed. Depending upon the rate at which switch 13 is actuated, it may be desirable :to encircle yleg 14 with a closed single-turn damping winding to prevent overshoot of the llux yadjustment effected 'by control winding 114.

ln an exemplary operation of the system of FIG. 1, the analog signal voltage Vi is applied to terminal lll, while switchesV ll, 13, 33 are momentarily closed. lf there is any difference AV between the then existing output voltage V0 andthe applied input voltage V1, the error signal voltage E, representing :an amplified version of this diierence, is applied to control win-ding M to pass a corresponding current through it.

Assuming that the core lo was, prior to the application of voltage E to the control winding, in a state of saturation in the positive or clockwise direction, and

that the magneto-motive force developed by circulation arcanos sa of current `in winding ld is in the negative sense, it is clear that the existing condition of saturation may be partially or entirely removed, or even reversed. When the intermediate or second leg 22 as well as the third leg 23 `are saturated, no additional flux can be developed about Iaperture 1S for linking the primary and secondary windings by coupling through the core material. lThe coupling and consequently the output voltage VO will then be at Va minimum. Hence, any change away from the condition of saturation will allow output voltage Vo to be increased toward V1. Actually, since the flux path circulating the main aperture i7 is the shortest and hence most responsive to excitation of winding lli, the range of ilux density variations ybetween saturation and non-saturation is eectively accomplished in the intermediate leg 22 with preferred operation.

A suitably large current in control Winding ld is then able to produce such a change from the saturated condition in leg 22 that the output voltage V0 is increased toward the input voltage Vi. As the output and input approach equality, the .error sign-al goes towmds zero and the core is left in the remanent state, which is required or a lux coupling between the primary and secondary windings suicient to produce such output voltage. When switches l, 13, 33 are then opened, the output voltage Vo remains constant indefinitely at Ithe set value, so long `as the reference signal from the supply 2S remains constant. During :a succeeding interval, the input signal may be again sampled and the remanent state oi the core reset by application of the error signal until the output voltage again is brought into correspondence lwith the sampled input voltage. ln this manner a continuous reading may be obtained from output meter 3d representing the last sampled value of the input signal, regardless of tirne elapsed s-ince the sampling operation.

It will be yappreciated that adjustment of the residual ux density in the intermediate leg Z2 of the core may 'be in a positive or negative sense depending upon whether the error signal is positive or negative, so that the output voltage may be in enact .correspondence `with the sampled input voltage in the zero to full scale range. It has been found that the core will remain in a desired condition of remanence when excitation of the control winding by the amplifier is terminated following a sample interval, where such interval is relatively short. Hence, the switch 1&3 may be closed at a rate of, say, 2 itc. Also, if desired, the control winding may be shorted at all times except during a sampling interval to preclude any change in magnetic state of the core due to switching transients. If desired, a shorting switch across coil 14 may be substituted for series switch i3 and closed at alternate Itimes. Of course, switches il, 33 need 'be closed only for isuch time as is required to effect the necessary change in magnetic state of the core. For a full scale change, -50 milliseconds has been found suitable.

In FIG. 2 there is shown 1a multichannel embodiment of the invention wherein ia pulse duna-.tion modulated (PDM) input signal is translated to obtain continuous indications of the channel values. To obtain an analog representation of the input signal channel values for application to one input of the differential amplifier l2, a translator 35 is connected between system input terminal 34 and the differential ampliiier. Translator 35 provides la pulse amplitude modulated (PAM) output, and for this purpose, may comprise an inverted ramp generator providing la decreasing voltage ramp which is initiated by the leading edge of the PDM pulses and locked substantially for the duration of the channel interval at the lower value existing upon arrival of Ithe trailing edge. In addition translator 35 may have Ia gated output for xing the output duration of the error voltage at ythe locked value. To gate the output of the translator, as well `as to reset it just prior to .the end of the channel interval, a gating circuit 36 may the provided which is responsive to the leading edges of the PDM input to provide delayed gate pulses to the translater.

in lieu of switch 13, there is provided a chopper 3S which chops the error signal output of the differential amplifier to Zero at a rate of, say, 2 kc. The chopper may be gated on during the successive channel intervals when the amplitude modulated pulses `are `applied to amplifier l2 by a suitable connection to gating circuit 36. The output of chopper 33 is applied in common to error signal poles ot channel relays it? in parallel relation, each relay being of the double pole type and only one relay being closed during any sampling or data channel interval. As illustrated, for example, the contacts or" relay hib are closed to connect chopper 3S 4to the con-trol winding input of transiiuxor dll for channel No. l. Sequential closing of the relays is controlled by ring counter 45 which is stepped by leading edges of the PDM input and reset for synchronization with the transmitter-source of the PDM input by synchronization detector For example, detector 46 may be selectively responsive to a double channel sync pulse and may comprise a Schmitt trigger for providing a reset pulse to the ring counter.

Additional .transtluxors may be provided, such as 42, for additional channels, as well las for calibration purposes. Like transfluxor 4i, their primary windings are connected in common (series) with the output of oscillator i3 (corresponding to A.C. supply Z8) and their secondary windings are connected via respective channel relay contacts to a common junction Iwith the remaining input 'terminal oi diiierential amplifier l2 to apply rectified feedback thereto. The boxes representing transux-ors di .and 42. will be understood to include rectiiiers corresponding to rectifier 29. Their rectified outputs are supplied to corresponding output meters 3Q.

Por purposes of caribration the zero reference channel relay connects chopper 38 with a Itransiiuxor 50 having its primary connected to oscillator i3 and its secondary coupled through a rectifier to a zero reference adjusting circuit in translator 35. For example, the initial value of the ramp voltage may be responsive to the output of transiluxor 5d to provide automatic zero calibration when a zero reference pulse is` received at the input. The translator output corresponding to the width of the Zero reference pulse is compared with a Zero reference voltage 'from regulated supply 5l. Similarly, a full scale transliuxor may be connected through a channel relay in suitable ysequence for adjusting the slope of the ramp employed in the translator 35, when a full scale pulse is received.

in general, the operation of the system shown in FIGURE 2 corresponds to that of FIGURE l but with a periodicity slaved to the incoming PDM signal. By the synchronous operation oi channel relays dit, the magnetic states of the respective transfluxors are periodically reset by the error signal between the corresponding outputs and PAM inputs lso that each output meter accurately and continuously indicates a proper channel value. When the zero or full scale values are applied to the dilierential ampliiier, any difference between such values and the voltages derived from the zero or full scale reference supplies, respectively, will result in automatic adjustment of calibration. By actuating chopper 38 only when both the PAM and feedback inputs are applied to the diiierential ampliiier i2, any false resetting of the transuxors will be avoided.

it will be understood that the invention is susceptible to a wide variety of modiiications and adaptations in many different applications. Accordingly, the invention is not to be limited to the embodiments illustrated and described, but is of a `scope defined in the appended claims.

What is ciaimed is:

l. An analog storage system comprising a plurality of transiiuxor units each haviny a multi-apertured core of rectangular hysteresis material, primary and secondary windings carried by a first portion of said core linking one aperture and a control Winding carried by a second portion of said core linking a second aperture to adjust fiux density in a core portion intermediate said apertures, means for passing regulated alternating current through each said primary winding to develop an output signal in the corresponding output winding `dependent upon flux coupling developed about said one aperture, a differential amplifier having one input to which the analog signal to be stored is applied, signal rectifying means coupled to the output windings of said transfiuxor units to develop a rectified version of the corresponding output signal for application to a second input of said differential amplifier, and switch means for synchronousl-y coupling the output winding of each succes-sive transiuxor unit with the second input of said dierential amplifier in sequence with coupling the output of -saird amplifier with the control winding of such successive transfiuxor units.

2. An analog storage system in accordance with claim 1 further comprising means for periodically reducing the output of said differential amplfier to Zero at a frequency lower than said alternating current asynchronously with respect to said switch means.

3. A system for storing in analog form data transmitted in successive channels of a PDM signal having a calibration channel, comprising means for translating said PDM signal into a PAM signal and including a circuit responsive to a calibration signal for correcting the correspondence between said PAM signal and said PDM signal, a plurality of transfiuxor unit-s each having a multi-apertured core of rectangular hysteresis material, primary and secondary windings carried by a first portion of said core linking one aperture and a control winding carried by a second portion of said core linking a second aperture to adjust fiuX density in a core portion intermediate said apertures, means for passing regulated alternating current through each said primary Winding to develop an output signal in the corresponding output winding dependent upon fiux coupling developed about said one aperture, a differential amplifier having one input to which said PAM signal is applied, signal reotifying means coupled to the output windings of said itransiiuxor units to develop a rectified version of the corresponding output signal for application lto a second input of said ydifferential amplier, a reference supply for providing a calibration Voltage, and switch means synchronized by said PDM signal for coupling said calibration voltage to the second input of said differential amplifier while coupling the output of said amplifier with the contnol winding of one of said transfluxor units to develop in its output winding a calibration signal for application to the correcting circuit of said translating means when the calibration channel of said PDM signal is applied thereto, and for sequentially coupling the output winding of other of said transiiuxor units with the second input of said differential amplifier while suc cessively coupling the output of said amplifier with the control Winding of said other transfluxor units, whereby the PAM signal output of said translating means is corrected for calibration and sai-d differential amplifier sets said other transfiuXo-r units in accordance with the `data transmitted in respective channels of Isaid PDM signal.

References @fated in the file of this patent UNITED STATES PATENTS 2,911,629 Wetzstein et al Nov. 3, 1959 2,990,540 Sublette et al. .inne 27, 1961 2,988,731 Kam Li June 13, 1961 3,021,072 Robinson Feb. 13, 19612 

1. AN ANALOG STORAGE SYSTEM COMPRISING A PLURALITY OF TRANSFLUXOR UNITS EACH HAVING A MULTI-APERTURED CORE OF RECTANGULAR HYSTERESIS MATERIAL, PRIMARY AND SECONDARY WINDINGS CARRIED BY A FIRST PORTION OF SAID CORE LINKING ONE APERTURE AND A CONTROL WINDING CARRIED BY A SECOND PORTION OF SAID CORE LINKING A SECOND APERTURE TO ADJUST FLUX DENSITY IN A CORE PORTION INTERMEDIATE SAID APERTURES, MEANS FOR PASSING REGULATED ALTERNATING CURRENT THROUGH EACH SAID PRIMARY WINDING TO DEVELOP AN OUTPUT SIGNAL IN THE CORRESPONDING OUTPUT WINDING DEPENDENT UPON FLUX COUPLING DEVELOPED ABOUT SAID ONE APERTURE, A DIFFERENTIAL AMPLIFIER HAVING ONE INPUT TO WHICH THE ANOLOG SIGNAL TO BE STORED IS APPLIED, SIGNAL RECTIFYING MEANS COUPLED TO THE OUTPUT WINDINGS OF SAID TRANSFLUXOR UNITS TO DEVELOP A RECTIFIED VERSION OF THE CORRESPONDING 